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Re: [Xen-devel] BUG: unable to handle kernel paging request - balloon_in

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] BUG: unable to handle kernel paging request - balloon_init - xen-4.1.0 -
From: Scott Garron <xen-devel@xxxxxxxxxxxxxxxxxx>
Date: Wed, 27 Apr 2011 19:45:42 -0400
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On 04/27/2011 04:09 PM, Konrad Rzeszutek Wilk wrote:
Duh! I meant this one:

[    0.316665] RIP: e030:[<ffffffff819a8aea>]  [<ffffffff819a8aea>]

Sorry about that. Can you also run your kernel with 'initcall_debug
loglevel=8' please?

     Ok, I've put what I came up with here:


     I also added a few pr_info() lines around the offending code to try
to get more of a handle of how far it is getting and what it's working
on at the time of failure:


diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index a065fda..b5f0650 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -488,10 +488,13 @@ static int __init balloon_init(void)
        extra_pfn_end = min(min(max_pfn, e820_end_of_ram_pfn()),
                            (unsigned long)PFN_DOWN(xen_extra_mem_start
+ xen_ex
+       pr_info("extra_pfn_end: 0x%x", extra_pfn_end); /* debug */
        for (pfn = PFN_UP(xen_extra_mem_start);
             pfn < extra_pfn_end;
             pfn += balloon_npages) {
+               pr_info("pfn: 0x%x", pfn); /* debug */
                page = pfn_to_page(pfn);
+               pr_info("page: 0x%p", page);  /* debug */
                /* totalram_pages doesn't include the boot-time
                   balloon extension, so don't subtract from it. */


     The new serial console output, with "initcall_debug loglevel=8" and
the pr_info() additions to the code can be found here:


... but I'll paste the part closest to the crash here for your convenience:

[    1.016663] calling  balloon_init+0x0/0x280 @ 1
[    1.016663] xen_balloon: Initialising balloon driver with page order 0.
[    1.033446] last_pfn = 0x1d9ff0 max_arch_pfn = 0x400000000
[    1.036663] extra_pfn_end: 0x1d9ff0
[    1.036663] pfn: 0x100000
[    1.036663] page: 0xffffea0003800000
[    1.036663] BUG: unable to handle kernel paging request at
[    1.036663] IP: [<ffffffff819a8b1f>] balloon_init+0x240/0x280
[    1.036663] PGD 18402067 PUD 18403067 PMD 0

     So the crash is happening within the first iteration of that for()
loop, presumably while calling __balloon_append(page).  That's as far as
I dove into it so far, but I figured I'd give you an update as to what
I've found and tried.

     Just for more information sake, I also tried booting this kernel as
a paravirt domU under the Debian Stable 2.6.32-5-xen-amd64 stock kernel
and Xen 4.1.0.  It booted without incident (aside from a ridiculously
long spew of printk's from my additions to that for() loop), so the
failure is specific to the kernel booting as a dom0.  That probably
doesn't narrow down much, but I figured it was noteworthy.

Scott Garron

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